A fuel cell has been proposed as a clean, efficient, and environmentally responsible power source for electric vehicles and various other applications. Individual fuel cells can be stacked together in series to form a fuel cell stack for various applications. The fuel cell stack is capable of supplying a quantity of electricity sufficient to power a vehicle. In particular, the fuel cell stack has been identified as a potential alternative for the traditional internal-combustion engine used in modern automobiles.
One type of fuel cell is the polymer electrolyte membrane (PEM) fuel cell. The PEM fuel cell includes three basic components: an electrolyte membrane; and a pair of electrodes, including a cathode and an anode. The electrolyte membrane is sandwiched between the electrodes to form a membrane-electrode-assembly (MEA). The MEA is typically disposed between porous diffusion media (DM), such as carbon fiber paper, which facilitates a delivery of reactants, such as hydrogen to the anode and oxygen to the cathode. An MEA and DM preassembled together with a subgasket for the separation of reactant fluids is known as a unitized electrode assembly (UEA).
In the electrochemical fuel cell reaction, the hydrogen is catalytically oxidized in the anode to generate free protons and electrons. The protons pass through the electrolyte to the cathode. The electrons from the anode cannot pass through the electrolyte membrane, and are instead directed as an electric current to the cathode through an electrical load, such as an electric motor. The protons react with the oxygen and the electrons in the cathode to generate water.
The electrolyte membrane is typically formed from a layer of ionomer. The electrodes of the fuel cell are generally formed from a finely-divided catalyst. The catalyst may be any electrocatalyst that catalytically supports at least one of an oxidation of hydrogen or methanol, and a reduction of oxygen for the fuel cell electrochemical reaction. The catalyst is typically a precious metal such as platinum or another platinum-group metal. The catalyst is generally disposed on a carbon support, such as carbon black particles, and is dispersed in an ionomer.
The electrolyte membrane, the electrodes, the DM, and a subgasket, for example, in the form of the UEA, are disposed between a pair of fuel cell plates. The pair of fuel cell plates constitutes an anode plate and a cathode plate. Each of the fuel cell plates may have a plurality of channels formed therein for distribution of the reactants and coolant to the fuel cell. The fuel cell plate is typically formed by a conventional process for shaping sheet metal such as stamping, machining, molding, or photo etching through a photolithographic mask, for example. In the case of a bipolar fuel cell plate, the fuel cell plate is typically formed from a pair of unipolar plates, which are then joined to form the bipolar fuel cell plate.
Known bipolar fuel cell plates have anode and cathode unipolar plates with substantially planar surfaces around the perimeters or edges of the plates. Typically, the unipolar plates are stamped from very thin metal sheets, for example, stainless steel sheets having a thickness of roughly 100 μm. The anode and cathode unipolar plates are also not welded together at the respective perimeters, and tend to splay apart. The bipolar fuel cell plates are undesirably subject to deformation of the edges of the unipolar plates due to poor handling and rough shipping. If the deformation is sufficiently large, the deformation results in a point load on the subgasket that separates adjacent fuel cells. The point load on the subgasket can cause cell-to-cell electrical shorting if the deformed edge pierces the subgasket and touches an adjacent bipolar fuel cell plate.
It has heretofore been known to use a plastic spacer frame that separates the perimeters of adjacent bipolar fuel cell plates in order to militate against cell-to-cell shorting, for example, as disclosed in U.S. patent application Ser. No. 12/859,343 to Miller et al. The known plastic spacer frame is heat sealed to the plate around the perimeter of the bipolar fuel cell plate, for example, by heat staking. This is just one possible method of assembly; a pressure sensitive adhesive (PSA), mechanical alignment, and loose laid configuration aligned over datum pins are other potential options. The thin metal sheets typically employed can make difficult the attaching of the plastic spacer frame to the bipolar fuel cell plates.
There is a continuing need for a fuel cell plate that militates against edge deformation and provides continuous supporting features for downstream process steps such as sealing and attaching the insulating spacer frame to the fuel cell plate.